The present invention pertains to electrostatic fluid dispensing apparatus, and more particularly pertains to electrostatic fluid dispensing nozzle modulators, nozzle modulator assemblies, and methods of electrostatic spraying.
In electrostatic fluid dispensing, a small amount of fluid is electrostatically charged and controllably dispensed in one or more continuous jets or streams or discontinuous paths of droplets. The term "fluid" is used herein to refer to liquids and to other flowable materials and to other materials made flowable by the application of heat or pressure. The term "fluid path" is used herein to refer broadly to ligaments, streams, jets, droplets, sheets and other continuous or discontinuous paths of the fluid.
Previous electrostatic spray nozzles are typically in the form of an electrified capillary, for example Winston, U.S. Pat. No. 3,060,429. In these nozzles, fluid is introduced through a small capillary port, typically about 0.001 inches in diameter, at a pressure which in itself is insufficient to produce flow. By imposing an electric field between the extremity of the nozzle and a conductive, nearby (typically one-quarter inch distant) substrate, small jets of charged liquid can be forced to fire. Electrodes placed adjacent to the jet's path can be impressed with a voltage to steer the jet to provide ink patterns on a paper substrate.
The multi-point nozzle found in Escallon, et al, U.S. Pat. No. 4,749,125, obviates the need for small orifices and limited throughputs. This nozzle has found many useful applications in areas as diverse as high speed metal lubrication and placing chemical treatments on foodstuffs or plants. Such nozzles, with current power sources would be useful with throughput materials having resistivities down to about 10.sup.6 ohm-centimeters.
Other nozzles, such as the nozzles disclosed in an application for United States Letters Patent filed by Rodenberger and Hunnicutt filed contemporaneously herewith have found many useful applications similar to the Escallon nozzles with materials having resistivities below 10.sup.6 ohm-centimeters and surface tensions approaching that of deionized water.
However, all of these nozzles have the shortcoming that the dispensed material tends to lie in a planar trajectory for some distance from the nozzle, rather than quickly forming a homogeneous charged fog. As a consequence, objects close to the nozzle and irregular target objects are not coated with the desired uniformity. Unless an array of differently directed nozzles is used rather than a singular nozzle, irregular shapes such as lettuce leaves, waffle irons or the interior of tin cans would not be uniformly coated except along the firing line.
It is therefore highly desirable to provide an improved nozzle modulator, nozzle modulator assembly and coating method.
It is therefore highly desirable to provide a nozzle modulator, a nozzle modulator assembly, and an improved coating method which produce coatings from a single nozzle like that achieved using an array of differently directed nozzles.
It is also highly desirable to provide an improved nozzle modulator, an improved nozzle modulator assembly, and an improved coating method by which objects close to the nozzle and irregular objects can be coated with uniformity.
It is also highly desirable to provide an improved nozzle modulator, an improved nozzle modulator assembly, and an improved coating method in which a homogeneous charged fog may be provided comprising a plurality of similarly charged droplets moving in a variety of different directions.
It is also highly desirable to provide an improved nozzle modulator, an improved nozzle modulator assembly, and an improved coating method in which a homogeneous charged fog may be provided close to the nozzle.
It is finally highly desirable to provide an improved nozzle modulator, an improved nozzle modulator assembly, and an improved coating method which meet all of the above desired features.